Terahertz transmission of a Ba{sub 1{minus}{ital x}}K{sub {ital x}}BiO{sub 3} film probed by coherent time-domain spectroscopy
- Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States)
- Science and Technology Center for Superconductivity, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)
The complex transmission coefficient for millimeter and submillimeter waves incident on a Ba{sub 0.6}K{sub 0.4}BiO{sub 3} thin film (82 nm) has been measured over a frequency range of 200--1200 GHz at temperatures above and below {ital T}{sub {ital c}} using coherent time-domain spectroscopy. We observe a dramatic change in both the magnitude and phase of the terahertz transmission in the superconducting state caused by a rapid carrier condensation. Both the real ({sigma}{sub 1}) and imaginary ({sigma}{sub 2}) parts of the complex conductivity are determined directly from the amplitude and phase of the transmitted electric field without the need for a Kramers-Kroenig analysis. By fitting {sigma}{sub 2} in the framework of BCS theory, a superconducting gap 2{Delta}(0)=6.9 meV=3.8{ital k}{sub {ital B}}{ital T}{sub {ital c}} is obtained. Below {ital T}{sub {ital c}}, the {sigma}{sub 1} is rapidly enhanced for {omega}/2{pi}{lt}500 GHz, which is attributed to the BCS coherence effects. However, the conductivity exhibits monotonic temperature dependence and no clear {sigma}{sub 1}({ital T}) peak is observed throughout the frequency range measured. The high-frequency penetration depth ({similar_to}600 nm) is also extracted and discussed. Our results are consistent with a picture of BCS moderate coupling superconductivity in an intermediate to dirty limit.
- OSTI ID:
- 85763
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 52, Issue 5; Other Information: PBD: 1 Aug 1995
- Country of Publication:
- United States
- Language:
- English
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